This invention generally relates to protection devices, and more specifically to an integral current, temperature, and pressure sensitive protection device especially well suited for use with hermetically and semi-hermetically sealed motor-compressor units.
The utilization of electrically driven hermetically and semi-hermetically sealed motor-compressor units has become increasingly prevalent in recent years, particularly in refrigeration applications where the motor-compressor units are employed to compress refrigerant vapor. Typically, these motor-compressor units are provided with protection systems to protect the units against excessive pressure, temperature, and current, and numerous such systems are well known in the art.
While these prior art systems operate effectively, it is believed that they suffer various disadvantages. For example, these protection systems conventionally employ a plurality of separate devices, with each device sensing one or at most two parameters and terminating operation of the motor-compressor unit when a sensed parameter exceeds a preset value. With this arrangement, a separate operation is needed to install each sensing device and, should it be necessary to remove the devices, a separate operation is similarly needed to remove each sensing device. This tends to result in relatively high assembly and maintenance costs for the protection systems.
In addition, the prior art protection systems commonly involve conflicting goals or considerations. In particular, to optimize accuracy, a sensor such as a motor temperature sensor may be located inside the motor-compressor unit. With a hermetically or semi-hermetically sealed motor-compressor unit, though, this makes it difficult to remove the sensor and may make it practically impossible to replace the sensor without replacing the entire motor-compressor unit. Locating the sensor outside the motor-compressor unit substantially facilitates removing the sensor, but this usually adversely affects the accuracy of the sensor. While many prior art protection systems provide a satisfactory compromise between these conflicting goals, it is nonetheless felt that a better compromise may be achieved.